The present invention relates to underwater acoustics, more particularly to methods and apparatuses, such as used in association with marine vessels, for effecting passive sonar to detect or locate underwater objects.
According to typical current practice of passive sonar by the United States Navy, broadband coverage is provided by a combination of: (i) one or more hull arrays of sonar sensors (hull-mounted, e.g., mounted conformally on the body and/or on the bow); and, (ii) one or more towed arrays of sonar sensors. The towed sensor arrays provide the performance at low frequencies, but their handling and maintenance make them impractical under some conditions. A towed sensor array also suffers because it cannot discriminate between contacts on the right or left of the array.
Some marine vessels are provided on their hull exteriors with mechanically compliant coatings. These mechanically compliant coatings are sometimes referred to simply as “compliant” coatings, and are also referred to as “flexible” or “soft” coatings. A mechanically compliant coating is typically an outside hull coating that is characterized by a significant degree of elasticity (e.g., viscoelasticity). A mechanically compliant hull coating, typically composed of a polymeric (e.g., elastomeric) material, tends to restrict or impede the attachment of instrumentation to the hull. Typical hull-mounted acoustical sensors require complex and expensive baffling, as it is impractical to directly couple the sensors with the mechanically compliant coatings. The baffles serve to reduce the effects of the ship's noise on the sensors, but are undesirably limiting in terms of size and frequency coverage of the sensors.